json_prettifier.rb

require "digest/md5"
require "set"
require "yajl"

module Steno
end

class Steno::JsonPrettifier
  FIELD_ORDER = %w[
    timestamp
    source
    process_id
    thread_id
    fiber_id
    location
    data
    log_level
    message
  ]

  MIN_COL_WIDTH = 14

  class ParseError < StandardError
  end

  def initialize(excluded_fields = [])
    @time_format = "%Y-%m-%d %H:%M:%S.%6N"
    @excluded_fields = Set.new(excluded_fields)
    @max_src_len = MIN_COL_WIDTH
  end

  def prettify_line(line)
    begin
      json_record = Yajl::Parser.parse(line)
    rescue Yajl::ParseError => e
      raise ParseError, e.to_s
    end

    format_record(json_record)
  end

  protected

  def format_record(record)
    record ||= {}
    fields = []

    FIELD_ORDER.each do |field_name|
      next if @excluded_fields.include?(field_name)

      exists = nil
      pred_meth = "check_#{field_name}".to_sym
      if respond_to?(pred_meth)
        exists = send(pred_meth, record)
      elsif record.respond_to?(:has_key?)
        exists = record.has_key?(field_name)
      else
        msg = "Expected the record to be a hash, but received: #{record.class}."
        raise ParseError, msg
      end

      if exists
        fields << send("format_#{field_name}".to_sym, record)
      else
        fields << "-"
      end
    end

    fields.join(" ") + "\n"
  end

  def format_timestamp(record)
    Time.at(record["timestamp"]).strftime(@time_format)
  end

  def format_source(record)
    @max_src_len = [@max_src_len, record["source"].length].max
    record["source"].ljust(@max_src_len)
  end

  def format_process_id(record)
    "pid=%-5s" % [record["process_id"]]
  end

  def format_thread_id(record)
    "tid=%s" % [shortid(record["thread_id"])]
  end

  def format_fiber_id(record)
    "fid=%s" % [shortid(record["fiber_id"])]
  end

  def check_location(record)
    %w[file lineno method].reduce(true) { |ok, k| ok && record.has_key?(k) }
  end

  def format_location(record)
    parts = record["file"].split("/")

    trimmed_filename = nil
    if parts.size == 1
      trimmed_filename = parts[0]
    else
      trimmed_filename = parts.slice(-2, 2).join("/")
    end

    "%s/%s:%s" % [trimmed_filename, record["method"], record["lineno"]]
  end

  def check_data(record)
    record["data"].is_a?(Hash)
  end

  def format_data(record)
    record["data"].map { |k, v| "#{k}=#{v}" }.join(",")
  end

  def format_log_level(record)
    "%7s" % [record["log_level"].upcase]
  end

  def format_message(record)
    "-- %s" % [record["message"]]
  end

  def shortid(data)
    return "-" if data.nil?
    digest = Digest::MD5.hexdigest(data.to_s)
    digest[0, 4]
  end
end